ICS - Microbiology and infectious disease Flashcards
Define pathogen
Organism that causes or is capable of causing disease
Define commensal
Organism which colonises the host but causes no disease in normal circumstances
Define opportunist pathogen
Microbe that only causes disease if host defences are compromised
Define asymptomatic carriage
When a pathogen is carried harmlessly at.a tissue site where it causes no disease
What colour does gram stain present when it is positive?
Purple
What colour does negative gram stain bacteria present?
Pink
Describe gram negative bacteria
2 membranes - an inner and outer membrane, which are separated by lipoprotein, periplasmic, space and peptidoglycan
What genetic mutations can appear in bacteria?
Base substitution, deletion, transfer
What gene transfers can occur in bacteria?
Transformation, transduction, conjugation
Describe how to perform a gram stain
Apply a primary stain such as crystal violet to heat fixed bacteria
Add iodide which binds to crystal violet and helps fix It to the cell wall
Decolourise with ethanol or acetone
Counterstain with safranin
What is the purpose of the coagulase test?
Distinguishes S.aureus from other staphylococci - coagulase positive
What is Lancefield grouping?
A method of grouping catalyse negative, coagulase negative bacteria based on bacterial carbohydrate cell surface antigens
How do proteobacteria appear?
Gram-negative rod shaped
How do bacteroids appear?
Gram-negative rod shaped
How does chlamydia appear?
Gram-negative round pleimorphic
How do spirochetes appear?
Gram-negative spiral
What are the 3 groups of worms?
Nematodes, Trematodes, Cestodes
What is the pre-patent period?
The interval between infection and the appearance of eggs in the stool
What is the purpose of acid fast bacilli?
Stain used to identify organisms with wax-like, thick cell walls e.g. mycobacteria (resistant to gram stain)
What are the characteristics of viruses?
Non-cellular structure (no membranes or organelles)
Consist of an outer protein coat
Come in a variety of shapes
What are the 6 stages of viral replication?
Attachment Cell entry Interaction with host cells Replication Assembly Release
How do viruses cause disease?
Damage by direct destruction, modification of his cell structure or through cell proliferation
What is dimorphic fungi?
Fungi that exists as both yeast and moulds, switching between the two when conditions suit
Via what routes can bacteria enter the host?
Respiratory tract, GI tract, GU tract or skin breaks
